The present invention relates to the field of electrotechnology and electronics, in particular, components based on acoustic surface waves, such as bandpass filters with a relative bandwidth on the order of 0.1 percent, as well as oscillators.
Resonator filter cascades are known, for which at least two transversely coupled resonator filters, which are composed of several resonator structures, which are disposed next to one another, and form a waveguide for acoustic surface waves, are connected with one another so that each of the two transversely coupled resonator filters contains transducers, which include bus bars and electrode fingers and are referred to as coupling transducers and are connected over electrically conducting connections with a coupling transducer of a different transversely coupled resonator filter. Transducers, which are not coupling transducers, an input transducer in the case of one of the transversely coupled resonator filters—optionally as a parallel connection—and, in an analogous manner, an output transducer in the case of the other transversely resonator filter.
A special embodiment (G. Martin, B. Wall, R. Kunze, M. Weihnacht, Proceedings 1993 IEEE Ultrasonics Symposium, pages 35-39) contains four transducers, two of which are connected in parallel. FIG. 1 of this paper shows, a not cascaded, transversely coupled resonator filter However, a use of such transversely coupled resonator filters in a filter cascade is explicitly mentioned. If transducers of different individual filters, connected in parallel in this filter cascade, are connected electrically conducting with one another, then this means that in each case two transducers are operated as a parallel connection as coupling transducers
In the case of a further, special embodiment (DE 42 27 362), a resonator filter cascade consists of two transversely coupled resonator filters. Coupling transducers of various transversely coupled resonator filters are connected with one another over a pair of electrically conducting connections, called cascade connections. A complex coupling resistance is connected between these connections. In the event that this complex coupling resistance is a coil, called a coupling coil, the cascading attenuation, resulting from the mismatching of the cascade connection, is reduced and, consequently, the insertion attenuation of the resonator filter cascade is decreased.
This solution has the disadvantage that the use of coupling coils results in too high a cost when the resonator filter cascades are used in electronic circuits.